Starts a file read operation, reading bytes from a file (or pipe). More...

#include <Async.h>

Inheritance diagram for SC::AsyncFileRead:

Classes
struct	CompletionData

struct	Result

Public Member Functions
uint64_t	getOffset () const
	The file/pipe descriptor handle to read data from.

void	setOffset (uint64_t fileOffset)
	Sets the offset in bytes at which start reading.

Result	start (AsyncEventLoop &eventLoop)
	Shortcut for AsyncEventLoop::start.

Public Member Functions inherited from SC::AsyncRequest
void	setDebugName (const char *newDebugName)

void	executeOn (AsyncSequence &sequence)
	Adds the request to be executed on a specific AsyncSequence.

Result	executeOn (AsyncTaskSequence &task, ThreadPool &pool)
	Adds the request to be executed on a specific AsyncTaskSequence.

void	disableThreadPool ()
	Disables the thread-pool usage for this request.

	AsyncRequest (Type type)
	Constructs a free async request of given type.

Result	stop (AsyncEventLoop &eventLoop, Function< void(AsyncResult &)> *afterStopped=nullptr)
	Ask to stop current async operation.

bool	isFree () const
	Returns `true` if this request is free.

bool	isCancelling () const
	Returns `true` if this request is being cancelled.

bool	isActive () const
	Returns `true` if this request is active or being reactivated.

Type	getType () const
	Returns request type.

Result	start (AsyncEventLoop &eventLoop)
	Shortcut for AsyncEventLoop::start.

void	setUserFlags (uint16_t externalFlags)
	Sets user flags, holding some meaningful data for the caller.

uint16_t	getUserFlags () const
	Gets user flags, holding some meaningful data for the caller.

Function< void(AsyncResult &)> *	getCloseCallback ()
	Returns currently set close callback (if any) passed to AsyncRequest::stop.

const Function< void(AsyncResult &)> *	getCloseCallback () const

Public Attributes
Function< void(Result &)>	callback

Span< char >	buffer
	Callback called when some data has been read from the file into the buffer.

FileDescriptor::Handle	handle
	The writeable span of memory where to data will be written.

Public Attributes inherited from SC::AsyncRequest
AsyncRequest *	next = nullptr

AsyncRequest *	prev = nullptr

Friends
struct	AsyncEventLoop

Additional Inherited Members
Public Types inherited from SC::AsyncRequest
enum class	Type : uint8_t { LoopTimeout , LoopWakeUp , LoopWork , ProcessExit , SocketAccept , SocketConnect , SocketSend , SocketReceive , SocketClose , FileRead , FileWrite , FileClose , FilePoll }
	Type of async request. More...

Protected Member Functions inherited from SC::AsyncRequest
Result	checkState ()

void	queueSubmission (AsyncEventLoop &eventLoop)

AsyncTaskSequence *	getTask ()

Protected Attributes inherited from SC::AsyncRequest
AsyncSequence *	sequence = nullptr

Detailed Description

Starts a file read operation, reading bytes from a file (or pipe).

Callback will be called when the data read from the file (or pipe) is available.
Call AsyncRequest::executeOn to set a thread pool if this is a buffered file and not a pipe. This is important on APIs with blocking behaviour on buffered file I/O (all apis with the exception of io_uring).

File library can be used to open the file and obtain a file (or pipe) descriptor handle.

Note: Pipes or files opened using Posix O_DIRECT or Windows FILE_FLAG_WRITE_THROUGH & FILE_FLAG_NO_BUFFERING should instead avoid using the Task parameter for best performance.

When not using the Task remember to:

Open the file descriptor for non-blocking IO (SC::File::OpenOptions::blocking == false)
Call SC::AsyncEventLoop::associateExternallyCreatedFileDescriptor on the file descriptor

Additional notes:

When reactivating the AsyncRequest, remember to increment the offset (SC::AsyncFileRead::offset)
SC::AsyncFileRead::CompletionData::endOfFile signals end of file reached
io_uring backend will not use thread pool because that API allows proper async file read/writes

// Assuming an already created (and running) AsyncEventLoop named `eventLoop`
// ...
 
// Assuming an already created threadPool named `eventLoop
// ...
 
// Open the file
FileDescriptor fd;
File::OpenOptions options;
options.blocking = true; // AsyncFileRead::Task enables using regular blocking file descriptors
SC_TRY(File(fd).open("MyFile.txt", File::ReadOnly, options));
 
// Create the async file read request and async task
AsyncFileRead asyncReadFile;
asyncReadFile.callback = [&](AsyncFileRead::Result& res)
{
    Span<char> readData;
    if(res.get(readData))
    {
        if(res.completionData.endOfFile)
        {
            // Last callback invocation done when end of file has been reached
            // - completionData.endOfFile is == true
            // - readData.sizeInBytes() is == 0
            console.print("End of file reached");
        }
        else
        {
            // readData is a slice of receivedData with the received bytes
            console.print("Read {} bytes from file", readData.sizeInBytes());
            
            // OPTIONAL: Update file offset to receive a different range of bytes
            res.getAsync().setOffset(res.getAsync().getOffset()  + readData.sizeInBytes());
            
            // IMPORTANT: Reactivate the request to receive more data
            res.reactivateRequest(true);
        }
    }
    else
    {
        // Some error occurred, check res.returnCode
    }
};
char buffer[100] = {0};
asyncReadFile.buffer = {buffer, sizeof(buffer)};
// Obtain file descriptor handle and associate it with event loop
SC_TRY(fd.get(asyncReadFile.handle, Result::Error("Invalid handle")));
 
// Start the operation on a thread pool
AsyncTaskSequence asyncFileTask;
SC_TRY(asyncReadFile.executeOn(asyncFileTask, threadPool));
SC_TRY(asyncReadFile.start(eventLoop));
 
// Alternatively if the file is opened with blocking == false, AsyncFileRead can be omitted
// but the operation will not be fully async on regular (buffered) files, except on io_uring.
//
// SC_TRY(asyncReadFile.start(eventLoop));

Member Function Documentation

◆ getOffset()

uint64_t SC::AsyncFileRead::getOffset ( ) const

inline

The file/pipe descriptor handle to read data from.

Use SC::FileDescriptor or SC::PipeDescriptor to open it.

Returns the last offset set with AsyncFileRead::setOffset

◆ setOffset()

void SC::AsyncFileRead::setOffset ( uint64_t fileOffset )

inline

Sets the offset in bytes at which start reading.

Note: Setting file offset when reading is only possible on seekable files

◆ start()

Result SC::AsyncRequest::start ( AsyncEventLoop & eventLoop )

Shortcut for AsyncEventLoop::start.

Member Data Documentation

◆ buffer

Span<char> SC::AsyncFileRead::buffer

Callback called when some data has been read from the file into the buffer.

◆ handle

FileDescriptor::Handle SC::AsyncFileRead::handle

The writeable span of memory where to data will be written.

The documentation for this struct was generated from the following file:

Async.h

Classes

Public Member Functions

Public Attributes

Friends

Additional Inherited Members